Products manufactured from webs such as paper toweling, paper tissue and the like typically are perforated to facilitate the tearing of sheets from a roll. Perforations may be formed using mechanical apparatus. In conventional operations, a moving blade is employed to perforate a traveling paper web. As the paper web passes between the moving blade and a stationary anvil, the blade is positioned perpendicular to the traveling paper web. As the paper web moves, the blade rubs against the anvil to perforate the paper. This process occurs at relatively high speed.
A knife roll having machined grooves also may be employed in the perforating process. A perforating blade may be provided in each groove. Such blades may be mounted in rows along the periphery of the knife roll. The distance between blade rows corresponds to the distance between perforations on the web. Bonding areas or “bonds” are formed upon the web by slots in the perforating blade. As the blade rubs against the paper web on the stationary anvil, the blade cuts the paper web at points where the blade touches the paper web. Slots in the blade prevent certain areas of the paper web from being cut. The uncut areas bond the paper, preventing the paper from tearing entirely.
Several U.S. patents disclose means of imparting perforations to a roll of paper. U.S. Pat. No. 6,010,090 to Bushmaker et al. discloses an elongated web of paper perforated along a plurality of transverse lines to provide bands of web areas having relatively high tensile strength.
U.S. Pat. No. 5,755,654 to Schulz et al. is directed to an apparatus and method for pinch perforating a multi-ply web material to increase the perforation ply bond retention. A roll mounted perforator blade cooperates with a beveled anvil to produce perforation ply bonds perpendicular to the length of the multiple plies of web material.
There are drawbacks to currently known methods for perforating web or paper sheet materials. Forces generated between the blade and anvil sometimes cause vibrations which are detrimental to the overall processing of the web. Furthermore, there are relatively strict speed limitations using currently available mechanical mechanisms. At fast web processing speeds, unacceptably high levels of vibration may be generated, which may cause imperfections, web breaks or machine malfunctions. High levels of vibration between the perforation roll and the head are undesirable.
One disadvantage of current equipment designs is that such designs cannot quickly be changed to accommodate different sheet lengths on a roll without expending large amounts of time and effort to reconfigure or change out mechanical equipment. To change sheet length on a roll of paper which is being manufactured, the papermaking apparatus typically must be stopped, and a 3-4 hour procedure of changing out and re-adjusting equipment is sometimes necessary. Furthermore, periodic replacement of blades causes lost production and down time. Such down time is costly in terms of manpower and lost production.
What is needed in the industry is a system, apparatus and method of severing or perforating a web of material in a way that does not result in equipment vibration or failure at high web processing speeds. A system that is capable of severing or perforating a web in a manner that requires less equipment maintenance would be desirable. A system that does not require numerous blade changes, and is capable of cutting or perforating a web at fast processing speeds would be desirable. Furthermore, a system that is capable of changing bond patterns, sheet lengths, and the material weight to be severed in a short period of time would be desirable.